How is This Bank Splitting Apart it's Payment Distribution?
$begingroup$
I have a credit card and I'm trying to calculate future interest charges per month. I have 4 months of statements that I have had to reverse engineer their math for. It took me a few days, but I finally figured out this banks algorithms for calculating their interest (I tried to get their help, but nobody could figure it out lol... yeah...).
However I am stuck on one part I can't figure out. They break apart the payment into proportional parts. According to them, they're putting the majority towards the soonest promotional end date is all I got from them. It seems that each charge/balance has it's own weight to it.
So it's deferred interest, so the payment amount is not tied to any interestinterest calculations. Just focusing on one month, we have the following:
$$ text{Payment Amount:}quad text{$25.00}quadqquadqquad qquadqquadqquad qquadqquad$$
$$ text{Before payment:} quad text{$975,}quad quad ; text{$800,} qquadtext{$17.98,} qquad text{$74.99} $$
$$ text{After payment:}; quad text{$961.94,} quad text{$789.30,}quadtext{$17.74,} qquad text{$73.99} $$
$$ text{Difference of:}; qquad text{$13.06,} quad text{$10.70,}qquadtext{$0.24,} qquad text{$1.00} $$
The $975's deferment date ends 9/15/2018. All the rest end on 10/16/2018. I can't even think of where to start with this one, maybe my mind is zapped from figuring out their crazy system for their interest, but any help is greatly appreciated.
Thanks!
(Probably not needed for this calculation, but this months statement is from 10/17/2018 to the end of 11/15/2018, with the payment on 11/08/2018.)
finance
asked Dec 22 '18 at 0:22
intwarriorintwarrior
103
$endgroup$
add a comment |
$begingroup$
I have a credit card and I'm trying to calculate future interest charges per month. I have 4 months of statements that I have had to reverse engineer their math for. It took me a few days, but I finally figured out this banks algorithms for calculating their interest (I tried to get their help, but nobody could figure it out lol... yeah...).
However I am stuck on one part I can't figure out. They break apart the payment into proportional parts. According to them, they're putting the majority towards the soonest promotional end date is all I got from them. It seems that each charge/balance has it's own weight to it.
So it's deferred interest, so the payment amount is not tied to any interestinterest calculations. Just focusing on one month, we have the following:
$$ text{Payment Amount:}quad text{$25.00}quadqquadqquad qquadqquadqquad qquadqquad$$
$$ text{Before payment:} quad text{$975,}quad quad ; text{$800,} qquadtext{$17.98,} qquad text{$74.99} $$
$$ text{After payment:}; quad text{$961.94,} quad text{$789.30,}quadtext{$17.74,} qquad text{$73.99} $$
$$ text{Difference of:}; qquad text{$13.06,} quad text{$10.70,}qquadtext{$0.24,} qquad text{$1.00} $$
The $975's deferment date ends 9/15/2018. All the rest end on 10/16/2018. I can't even think of where to start with this one, maybe my mind is zapped from figuring out their crazy system for their interest, but any help is greatly appreciated.
Thanks!
(Probably not needed for this calculation, but this months statement is from 10/17/2018 to the end of 11/15/2018, with the payment on 11/08/2018.)
finance
asked Dec 22 '18 at 0:22
intwarriorintwarrior
103
$endgroup$
add a comment |
$begingroup$
I have a credit card and I'm trying to calculate future interest charges per month. I have 4 months of statements that I have had to reverse engineer their math for. It took me a few days, but I finally figured out this banks algorithms for calculating their interest (I tried to get their help, but nobody could figure it out lol... yeah...).
However I am stuck on one part I can't figure out. They break apart the payment into proportional parts. According to them, they're putting the majority towards the soonest promotional end date is all I got from them. It seems that each charge/balance has it's own weight to it.
So it's deferred interest, so the payment amount is not tied to any interestinterest calculations. Just focusing on one month, we have the following:
$$ text{Payment Amount:}quad text{$25.00}quadqquadqquad qquadqquadqquad qquadqquad$$
$$ text{Before payment:} quad text{$975,}quad quad ; text{$800,} qquadtext{$17.98,} qquad text{$74.99} $$
$$ text{After payment:}; quad text{$961.94,} quad text{$789.30,}quadtext{$17.74,} qquad text{$73.99} $$
$$ text{Difference of:}; qquad text{$13.06,} quad text{$10.70,}qquadtext{$0.24,} qquad text{$1.00} $$
The $975's deferment date ends 9/15/2018. All the rest end on 10/16/2018. I can't even think of where to start with this one, maybe my mind is zapped from figuring out their crazy system for their interest, but any help is greatly appreciated.
Thanks!
(Probably not needed for this calculation, but this months statement is from 10/17/2018 to the end of 11/15/2018, with the payment on 11/08/2018.)
finance
asked Dec 22 '18 at 0:22
intwarriorintwarrior
103
$endgroup$
I have a credit card and I'm trying to calculate future interest charges per month. I have 4 months of statements that I have had to reverse engineer their math for. It took me a few days, but I finally figured out this banks algorithms for calculating their interest (I tried to get their help, but nobody could figure it out lol... yeah...).
However I am stuck on one part I can't figure out. They break apart the payment into proportional parts. According to them, they're putting the majority towards the soonest promotional end date is all I got from them. It seems that each charge/balance has it's own weight to it.
So it's deferred interest, so the payment amount is not tied to any interestinterest calculations. Just focusing on one month, we have the following:
$$ text{Payment Amount:}quad text{$25.00}quadqquadqquad qquadqquadqquad qquadqquad$$
$$ text{Before payment:} quad text{$975,}quad quad ; text{$800,} qquadtext{$17.98,} qquad text{$74.99} $$
$$ text{After payment:}; quad text{$961.94,} quad text{$789.30,}quadtext{$17.74,} qquad text{$73.99} $$
$$ text{Difference of:}; qquad text{$13.06,} quad text{$10.70,}qquadtext{$0.24,} qquad text{$1.00} $$
The $975's deferment date ends 9/15/2018. All the rest end on 10/16/2018. I can't even think of where to start with this one, maybe my mind is zapped from figuring out their crazy system for their interest, but any help is greatly appreciated.
Thanks!
(Probably not needed for this calculation, but this months statement is from 10/17/2018 to the end of 11/15/2018, with the payment on 11/08/2018.)
finance
finance
asked Dec 22 '18 at 0:22
intwarriorintwarrior
103
asked Dec 22 '18 at 0:22
intwarriorintwarrior
103
asked Dec 22 '18 at 0:22
intwarriorintwarrior
103
asked Dec 22 '18 at 0:22
intwarriorintwarrior
103
asked Dec 22 '18 at 0:22
intwarriorintwarrior
103
103
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
$begingroup$
They've paid off the same proportion (rounded to the nearest cent) of each. Specifically, for a total payment of $p$, and amounts owing $x_1, ldots, x_n$, they've subtracted $$frac{px_k}{sumlimits_{i=0}^nx_i}$$ from each (rounding to the nearest penny, possibly with some check in there to make sure that the rounding all cancels out). Whatever they say about "putting the majority towards the soonest promotional end date", they aren't. Feel free to check the other months to be sure that this pattern holds up.
answered Dec 22 '18 at 0:40
user3482749user3482749
4,3211119
$endgroup$
$begingroup$
You are awesome, thank you! I can sleep peacefully tonight and finish my Excel sheet tomorrow. I likely won't get charged interest, but I'd still like to know to be able to project a just in case model. It's good practice/skill. And now I can make a full model that should match their statements.
$endgroup$
– intwarrior
Dec 22 '18 at 2:44
$begingroup$
Just out of curiosity, can you point me in the right direction to figure out how to do a similar checker to make sure they add up? Being a penny off isn't the end of the world, but I'd like to increase my programming skills too.
$endgroup$
– intwarrior
Dec 22 '18 at 2:51
$begingroup$
There's a few ways to do it, and I'm not sure which one your bank is doing. The easiest is probably to notice that if we round everything down to start with, the four remainders must add up to either 0 cents, 1 cent, 2 cents, or 3 cents (it has to be a whole number of cents, and you can't reach 4 cents). If it's 0 cents, then everything else adds up perfectly, so we don't need to do anything. If it's 1 cent, add 1 cent to the amount with the largest remainder. If it's 2 cents, add 1 cent to each of the 2 largest. If it's 3 cents, add one cent to each of the 3 largest.
$endgroup$
– user3482749
Dec 22 '18 at 11:49
$begingroup$
That's not quite what your bank is doing (they're a penny high on the first payment and a penny low on the second), but it's one of the more sensible ways to do it.
$endgroup$
– user3482749
Dec 22 '18 at 11:51
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "69"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3049031%2fhow-is-this-bank-splitting-apart-its-payment-distribution%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
They've paid off the same proportion (rounded to the nearest cent) of each. Specifically, for a total payment of $p$, and amounts owing $x_1, ldots, x_n$, they've subtracted $$frac{px_k}{sumlimits_{i=0}^nx_i}$$ from each (rounding to the nearest penny, possibly with some check in there to make sure that the rounding all cancels out). Whatever they say about "putting the majority towards the soonest promotional end date", they aren't. Feel free to check the other months to be sure that this pattern holds up.
answered Dec 22 '18 at 0:40
user3482749user3482749
4,3211119
$endgroup$
$begingroup$
You are awesome, thank you! I can sleep peacefully tonight and finish my Excel sheet tomorrow. I likely won't get charged interest, but I'd still like to know to be able to project a just in case model. It's good practice/skill. And now I can make a full model that should match their statements.
$endgroup$
– intwarrior
Dec 22 '18 at 2:44
$begingroup$
Just out of curiosity, can you point me in the right direction to figure out how to do a similar checker to make sure they add up? Being a penny off isn't the end of the world, but I'd like to increase my programming skills too.
$endgroup$
– intwarrior
Dec 22 '18 at 2:51
$begingroup$
There's a few ways to do it, and I'm not sure which one your bank is doing. The easiest is probably to notice that if we round everything down to start with, the four remainders must add up to either 0 cents, 1 cent, 2 cents, or 3 cents (it has to be a whole number of cents, and you can't reach 4 cents). If it's 0 cents, then everything else adds up perfectly, so we don't need to do anything. If it's 1 cent, add 1 cent to the amount with the largest remainder. If it's 2 cents, add 1 cent to each of the 2 largest. If it's 3 cents, add one cent to each of the 3 largest.
$endgroup$
– user3482749
Dec 22 '18 at 11:49
$begingroup$
That's not quite what your bank is doing (they're a penny high on the first payment and a penny low on the second), but it's one of the more sensible ways to do it.
$endgroup$
– user3482749
Dec 22 '18 at 11:51
add a comment |
$begingroup$
They've paid off the same proportion (rounded to the nearest cent) of each. Specifically, for a total payment of $p$, and amounts owing $x_1, ldots, x_n$, they've subtracted $$frac{px_k}{sumlimits_{i=0}^nx_i}$$ from each (rounding to the nearest penny, possibly with some check in there to make sure that the rounding all cancels out). Whatever they say about "putting the majority towards the soonest promotional end date", they aren't. Feel free to check the other months to be sure that this pattern holds up.
answered Dec 22 '18 at 0:40
user3482749user3482749
4,3211119
$endgroup$
$begingroup$
You are awesome, thank you! I can sleep peacefully tonight and finish my Excel sheet tomorrow. I likely won't get charged interest, but I'd still like to know to be able to project a just in case model. It's good practice/skill. And now I can make a full model that should match their statements.
$endgroup$
– intwarrior
Dec 22 '18 at 2:44
$begingroup$
Just out of curiosity, can you point me in the right direction to figure out how to do a similar checker to make sure they add up? Being a penny off isn't the end of the world, but I'd like to increase my programming skills too.
$endgroup$
– intwarrior
Dec 22 '18 at 2:51
$begingroup$
There's a few ways to do it, and I'm not sure which one your bank is doing. The easiest is probably to notice that if we round everything down to start with, the four remainders must add up to either 0 cents, 1 cent, 2 cents, or 3 cents (it has to be a whole number of cents, and you can't reach 4 cents). If it's 0 cents, then everything else adds up perfectly, so we don't need to do anything. If it's 1 cent, add 1 cent to the amount with the largest remainder. If it's 2 cents, add 1 cent to each of the 2 largest. If it's 3 cents, add one cent to each of the 3 largest.
$endgroup$
– user3482749
Dec 22 '18 at 11:49
$begingroup$
That's not quite what your bank is doing (they're a penny high on the first payment and a penny low on the second), but it's one of the more sensible ways to do it.
$endgroup$
– user3482749
Dec 22 '18 at 11:51
add a comment |
$begingroup$
They've paid off the same proportion (rounded to the nearest cent) of each. Specifically, for a total payment of $p$, and amounts owing $x_1, ldots, x_n$, they've subtracted $$frac{px_k}{sumlimits_{i=0}^nx_i}$$ from each (rounding to the nearest penny, possibly with some check in there to make sure that the rounding all cancels out). Whatever they say about "putting the majority towards the soonest promotional end date", they aren't. Feel free to check the other months to be sure that this pattern holds up.
answered Dec 22 '18 at 0:40
user3482749user3482749
4,3211119
$endgroup$
They've paid off the same proportion (rounded to the nearest cent) of each. Specifically, for a total payment of $p$, and amounts owing $x_1, ldots, x_n$, they've subtracted $$frac{px_k}{sumlimits_{i=0}^nx_i}$$ from each (rounding to the nearest penny, possibly with some check in there to make sure that the rounding all cancels out). Whatever they say about "putting the majority towards the soonest promotional end date", they aren't. Feel free to check the other months to be sure that this pattern holds up.
answered Dec 22 '18 at 0:40
user3482749user3482749
4,3211119
answered Dec 22 '18 at 0:40
user3482749user3482749
4,3211119
answered Dec 22 '18 at 0:40
user3482749user3482749
4,3211119
answered Dec 22 '18 at 0:40
user3482749user3482749
4,3211119
4,3211119
$begingroup$
You are awesome, thank you! I can sleep peacefully tonight and finish my Excel sheet tomorrow. I likely won't get charged interest, but I'd still like to know to be able to project a just in case model. It's good practice/skill. And now I can make a full model that should match their statements.
$endgroup$
– intwarrior
Dec 22 '18 at 2:44
$begingroup$
Just out of curiosity, can you point me in the right direction to figure out how to do a similar checker to make sure they add up? Being a penny off isn't the end of the world, but I'd like to increase my programming skills too.
$endgroup$
– intwarrior
Dec 22 '18 at 2:51
$begingroup$
There's a few ways to do it, and I'm not sure which one your bank is doing. The easiest is probably to notice that if we round everything down to start with, the four remainders must add up to either 0 cents, 1 cent, 2 cents, or 3 cents (it has to be a whole number of cents, and you can't reach 4 cents). If it's 0 cents, then everything else adds up perfectly, so we don't need to do anything. If it's 1 cent, add 1 cent to the amount with the largest remainder. If it's 2 cents, add 1 cent to each of the 2 largest. If it's 3 cents, add one cent to each of the 3 largest.
$endgroup$
– user3482749
Dec 22 '18 at 11:49
$begingroup$
That's not quite what your bank is doing (they're a penny high on the first payment and a penny low on the second), but it's one of the more sensible ways to do it.
$endgroup$
– user3482749
Dec 22 '18 at 11:51
add a comment |
$begingroup$
You are awesome, thank you! I can sleep peacefully tonight and finish my Excel sheet tomorrow. I likely won't get charged interest, but I'd still like to know to be able to project a just in case model. It's good practice/skill. And now I can make a full model that should match their statements.
$endgroup$
– intwarrior
Dec 22 '18 at 2:44
$begingroup$
Just out of curiosity, can you point me in the right direction to figure out how to do a similar checker to make sure they add up? Being a penny off isn't the end of the world, but I'd like to increase my programming skills too.
$endgroup$
– intwarrior
Dec 22 '18 at 2:51
$begingroup$
There's a few ways to do it, and I'm not sure which one your bank is doing. The easiest is probably to notice that if we round everything down to start with, the four remainders must add up to either 0 cents, 1 cent, 2 cents, or 3 cents (it has to be a whole number of cents, and you can't reach 4 cents). If it's 0 cents, then everything else adds up perfectly, so we don't need to do anything. If it's 1 cent, add 1 cent to the amount with the largest remainder. If it's 2 cents, add 1 cent to each of the 2 largest. If it's 3 cents, add one cent to each of the 3 largest.
$endgroup$
– user3482749
Dec 22 '18 at 11:49
$begingroup$
That's not quite what your bank is doing (they're a penny high on the first payment and a penny low on the second), but it's one of the more sensible ways to do it.
$endgroup$
– user3482749
Dec 22 '18 at 11:51
$begingroup$
You are awesome, thank you! I can sleep peacefully tonight and finish my Excel sheet tomorrow. I likely won't get charged interest, but I'd still like to know to be able to project a just in case model. It's good practice/skill. And now I can make a full model that should match their statements.
$endgroup$
– intwarrior
Dec 22 '18 at 2:44
$begingroup$
You are awesome, thank you! I can sleep peacefully tonight and finish my Excel sheet tomorrow. I likely won't get charged interest, but I'd still like to know to be able to project a just in case model. It's good practice/skill. And now I can make a full model that should match their statements.
$endgroup$
– intwarrior
Dec 22 '18 at 2:44
$begingroup$
Just out of curiosity, can you point me in the right direction to figure out how to do a similar checker to make sure they add up? Being a penny off isn't the end of the world, but I'd like to increase my programming skills too.
$endgroup$
– intwarrior
Dec 22 '18 at 2:51
$begingroup$
Just out of curiosity, can you point me in the right direction to figure out how to do a similar checker to make sure they add up? Being a penny off isn't the end of the world, but I'd like to increase my programming skills too.
$endgroup$
– intwarrior
Dec 22 '18 at 2:51
$begingroup$
There's a few ways to do it, and I'm not sure which one your bank is doing. The easiest is probably to notice that if we round everything down to start with, the four remainders must add up to either 0 cents, 1 cent, 2 cents, or 3 cents (it has to be a whole number of cents, and you can't reach 4 cents). If it's 0 cents, then everything else adds up perfectly, so we don't need to do anything. If it's 1 cent, add 1 cent to the amount with the largest remainder. If it's 2 cents, add 1 cent to each of the 2 largest. If it's 3 cents, add one cent to each of the 3 largest.
$endgroup$
– user3482749
Dec 22 '18 at 11:49
$begingroup$
There's a few ways to do it, and I'm not sure which one your bank is doing. The easiest is probably to notice that if we round everything down to start with, the four remainders must add up to either 0 cents, 1 cent, 2 cents, or 3 cents (it has to be a whole number of cents, and you can't reach 4 cents). If it's 0 cents, then everything else adds up perfectly, so we don't need to do anything. If it's 1 cent, add 1 cent to the amount with the largest remainder. If it's 2 cents, add 1 cent to each of the 2 largest. If it's 3 cents, add one cent to each of the 3 largest.
$endgroup$
– user3482749
Dec 22 '18 at 11:49
$begingroup$
That's not quite what your bank is doing (they're a penny high on the first payment and a penny low on the second), but it's one of the more sensible ways to do it.
$endgroup$
– user3482749
Dec 22 '18 at 11:51
$begingroup$
That's not quite what your bank is doing (they're a penny high on the first payment and a penny low on the second), but it's one of the more sensible ways to do it.
$endgroup$
– user3482749
Dec 22 '18 at 11:51
add a comment |
Thanks for contributing an answer to Mathematics Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3049031%2fhow-is-this-bank-splitting-apart-its-payment-distribution%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
